Add "bin/herald rule ..." to modify Herald rules from the CLI

Summary:
Depends on D20566. Ref T13298. See PHI1280. Currently, there's no clean way to disable problematic personal rules. This comes up occasionally and sometimes isn't really the best approach to solving a problem, but is a generally reasonable capability to provide.

Allow Herald rules (including personal rules) to be disabled/enabled via bin/herald rule ... --disable/--enable.

Test Plan: Used the CLI to disable and enable a personal rule.

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: jmeador

Maniphest Tasks: T13298

Differential Revision: https://secure.phabricator.com/D20567